Ethiopian police and farmers with flashlights searched a remote mountain area overnight for the missing plane carrying Rep. Mickey Leland (D-Tex.) and 13 other people. A daylong aerial search was suspended at dusk and will be resumed today. The Twin Otter aircraft disappeared Monday on its way from Addis Ababa to the Fugnido refugee camp near the border with Sudan, about 300 miles to the west. Leland, 44, has taken a keen interest in Africa's refugee problem. President Bush, saying Leland was on his sixth humanitarian mission in that part of the world, promised that his Administration will do all it can to help find the missing plane with Leland, eight other Americans and five Ethiopians.